Case Study: Electronic Power Steering Assist Pulley
Process: Conventional powder metallurgy
Apparent Hardness: HRB 36
Tensile Strength: 34,000 psi (230 MPa)
Yield Strength: 29,000 psi (200 MPa)
End Use and Function
The drive pulley is for an electronic power steering system that goes into assemblies found in the Ford Focus and Escape vehicle platforms and, at the time of its development, was one of the first powder metallurgy (PM) electronic power steering pulleys in service.
This unique iron–copper (FC-0200-24) six-level component, with 5° helical pulley teeth, has a 50-micrometre surface-profile tolerance, which requires tight tool-wear control. The part is formed net shape except for the inside diameter, threads, one bearing face, and two stamped flanges that are added using capacitive-discharge welding, which allows for precise control of the gap between the flanges and the teeth.
Conventional PM was chosen as the fabrication method because it offered far better precision than the die-cast alternative at a competitive price.